Custom Control and View Model Binding with Property Changed

Question

Edit. Example project that illustrates the problem, when I check a box, the ViewModel property does not update. http://1drv.ms/1JZJsNa

I have the following user control

it is a multi-select ComboBox. To construct this control, I have the following XAML:

The code behind has a number of DPs and is:

public partial class MultiSelectComboBoxView : UserControl, INotifyPropertyChanged
{
    private ObservableCollection nodeList;

    public MultiSelectComboBoxView()
    {
        InitializeComponent();
        nodeList = new ObservableCollection();
    }

    public static readonly DependencyProperty ShowAllCheckBoxProperty =
         DependencyProperty.Register("ShowAllCheckBox", typeof(bool), 
         typeof(MultiSelectComboBoxView), new PropertyMetadata(true));

    public static readonly DependencyProperty ItemsSourceProperty = 
        DependencyProperty.Register("ItemsSource", typeof(Dictionary), 
        typeof(MultiSelectComboBoxView), new FrameworkPropertyMetadata(
            null, new PropertyChangedCallback(MultiSelectComboBoxView.OnItemsSourceChanged)));

    public static readonly DependencyProperty SelectedItemsProperty =
     DependencyProperty.Register("SelectedItems", typeof(Dictionary), 
     typeof(MultiSelectComboBoxView), new FrameworkPropertyMetadata(null,
        new PropertyChangedCallback(MultiSelectComboBoxView.OnSelectedItemsChangedCallback)));

    public static readonly DependencyProperty TextProperty =
        DependencyProperty.Register("Text", typeof(string), typeof(MultiSelectComboBoxView), 
        new UIPropertyMetadata(string.Empty));

    public static readonly DependencyProperty DefaultTextProperty =
         DependencyProperty.Register("DefaultText", typeof(string), 
         typeof(MultiSelectComboBoxView), new UIPropertyMetadata(string.Empty));

    public bool ShowAllCheckBox
    {
        get { return (bool)GetValue(ShowAllCheckBoxProperty); }
        set { SetValue(ShowAllCheckBoxProperty, value); }
    }

    public Dictionary ItemsSource
    {
        get { return (Dictionary)GetValue(ItemsSourceProperty); }
        set { SetValue(ItemsSourceProperty, value); }
    }

    public Dictionary SelectedItems
    {
        get { return (Dictionary)GetValue(SelectedItemsProperty); }
        set { SetValue(SelectedItemsProperty, value); }
    }

    public string Text
    {
        get { return (string)GetValue(TextProperty); }
        set { SetValue(TextProperty, value); }
    }

    public string DefaultText
    {
        get { return (string)GetValue(DefaultTextProperty); }
        set { SetValue(DefaultTextProperty, value); }
    }

    private static void OnItemsSourceChanged(
        DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        MultiSelectComboBoxView control = (MultiSelectComboBoxView)d;
        control.DisplayInControl();
    }

    private static void OnSelectedItemsChangedCallback(
        DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        MultiSelectComboBoxView control = (MultiSelectComboBoxView)d;
        control.SelectNodes();
        control.SetText();
        control.CheckSetAllSelected();
    }

    private void CheckBox_Click(object sender, RoutedEventArgs e)
    {
        CheckBox clickedBox = (CheckBox)sender;
        if (clickedBox.Content.ToString() == "All")
        {
            if (clickedBox.IsChecked.Value)
            {
                foreach (ComboBoxNode node in nodeList)
                    node.IsSelected = true;
            }
            else
            {
                foreach (ComboBoxNode node in nodeList)
                    node.IsSelected = false;
            }
        }
        else
            CheckSetAllSelected();
        SetSelectedItems();
        SetText();
    }

    private void CheckSetAllSelected()
    {
        int selectedCount = 0;
        foreach (ComboBoxNode s in nodeList)
            if (s.IsSelected && s.Title != "All")
                selectedCount++;
        if (selectedCount == nodeList.Count - 1)
            nodeList.FirstOrDefault(i => i.Title == "All").IsSelected = true;
        else
            nodeList.FirstOrDefault(i => i.Title == "All").IsSelected = false;
    }

    private void SelectNodes()
    {
        foreach (KeyValuePair keyValue in SelectedItems)
        {
            ComboBoxNode node = nodeList.FirstOrDefault(i => i.Title == keyValue.Key);
            if (node != null)
                node.IsSelected = true;
        }
    }

    private void SetSelectedItems()
    {
        if (SelectedItems == null)
            SelectedItems = new Dictionary();
        SelectedItems.Clear();

        foreach (ComboBoxNode node in nodeList)
        {
            if (node.IsSelected && node.Title != "All")
            {
                if (this.ItemsSource.Count > 0)
                    SelectedItems.Add(node.Title, this.ItemsSource[node.Title]);
            }
        }

        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs("SelectedItems"));
    }

    private void DisplayInControl()
    {
        nodeList.Clear();
        if (this.ShowAllCheckBox && this.ItemsSource.Count > 0)
            nodeList.Add(new ComboBoxNode("All"));
        foreach (KeyValuePair keyValue in this.ItemsSource)
        {
            ComboBoxNode node = new ComboBoxNode(keyValue.Key);
            nodeList.Add(node);
        }
        MultiSelectCombo.ItemsSource = nodeList;
    }

    private void SetText()
    {
        if (this.SelectedItems != null)
        {
            StringBuilder displayText = new StringBuilder();
            foreach (ComboBoxNode s in nodeList)
            {
                if (s.IsSelected == true && s.Title == "All")
                {
                    displayText = new StringBuilder();
                    displayText.Append("All");
                    break;
                }
                else if (s.IsSelected == true && s.Title != "All")
                {
                    displayText.Append(s.Title);
                    displayText.Append(", ");
                }
            }
            this.Text = displayText.ToString().TrimEnd().TrimEnd(new char[] { ',' });
        }

        // Set DefaultText if nothing else selected.
        if (string.IsNullOrEmpty(this.Text))
            this.Text = this.DefaultText;
    }
    #endregion // Methods.

    public event PropertyChangedEventHandler PropertyChanged;
}

public class ComboBoxNode : INotifyPropertyChanged
{
    private string title;
    private bool isSelected;

    public ComboBoxNode(string title)
    {
        Title = title;
    }

    public string Title
    {
        get { return title; }
        set
        {
            title = value;
            NotifyPropertyChanged("Title");
        }
    }

    public bool IsSelected
    {
        get { return isSelected; }
        set
        {
            isSelected = value;
            NotifyPropertyChanged("IsSelected");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

}

with the backing ViewModel

public class MultiSelectComboBoxViewModel : PropertyChangedBase
{
    private Dictionary items;
    private Dictionary selectedItems;

    public MultiSelectComboBoxViewModel() { }
    public MultiSelectComboBoxViewModel(Dictionary items)
    {
        Items = items;
        SelectedItems = new Dictionary();
    }
    public MultiSelectComboBoxViewModel(Dictionary items,
        Dictionary selectedItems)
    {
        Items = items;
        SelectedItems = selectedItems;
    }

    public Dictionary Items
    {
        get { return items; }
        set
        {
            if (items == value)
                return;
            items = value;
            NotifyOfPropertyChange(() => Items);
        }
    }

    public Dictionary SelectedItems
    {
        get { return selectedItems; }
        set
        {
            if (selectedItems == value)
                return;
            selectedItems = value;
            NotifyOfPropertyChange(() => SelectedItems);
        }
    }
}

Now, I put this control in my some view, lets call it SomeView.xaml

and in my SomeViewModel.cs I have

public MultiSelectComboBoxViewModel SelectionMultiFilter { get; set; }

and populate the items via the ctor for the MultiSelectComboBoxViewModel, all items populate and I can get those selected via the SelectedItems property. Now my problem is that in SomeViewModel I cannot seem to subscribe to the PropertyChanged event for SelectionMultiFilter, it does not fire. Now I have done the obvious thing and changed my DP to include

public static readonly DependencyProperty SelectedItemsProperty =
    DependencyProperty.Register("SelectedItems", typeof(Dictionary), 
        typeof(MultiSelectComboBoxView), new FrameworkPropertyMetadata(null,
        new PropertyChangedCallback(MultiSelectComboBoxView.OnSelectedItemsChangedCallback)));

public Dictionary SelectedItems
{
    get { return (Dictionary)GetValue(SelectedItemsProperty); }
    set { SetValue(SelectedItemsProperty, value); }
}       

private static void OnSelectedItemsChangedCallback(
    DependencyObject o, DependencyPropertyChangedEventArgs e)
{
    MultiSelectComboBoxView control = (MultiSelectComboBoxView)d;
    control.SelectNodes();
    control.SetText();
    control.CheckSetAllSelected();

    MultiSelectComboBoxView d = o as MultiSelectComboBoxView;
    if (d != null) {
        d.OnSelectedItemsChanged();
    }
}

protected virtual void OnSelectedItemsChanged() {
    OnPropertyChanged("SelectedItems");
}

But this does not fire my PropertyChanged. Questions:

How can I get my consuming ViewModel to be notified when the SelectedItems of my MultiSelectComboBox get changed?
If I don't set the SelectedItems in the ctor for the MultiSelectComboBox when I set them from the consuming view model after, they don't update, how do I fix this?

Thanks for your time.

V&#225;clav Šv&#225;ra · Accepted Answer

I think dependecy property setter is not firing property changed notification.

public Dictionary SelectedItems
{
    get { return (Dictionary)GetValue(SelectedItemsProperty);}
    set { SetValue(SelectedItemsProperty, value); NotifyOfPropertyChange(() => Items);}
}

But anyway I am not able to investigate the code complete, when you put the breakpoint here:

public Dictionary SelectedItems
{
    get { return selectedItems; }
    set
    {
        if (selectedItems == value) <----------- here breakpoint
            return;
        selectedItems = value;
        NotifyOfPropertyChange(() => SelectedItems);
    }
}

will application break there after the one checkbox is changed? If not it looks that you are managing the collection as itself, so you should notified the change when collection is changed (implement ObservableDictionary)

Custom Control and View Model Binding with Property Changed

Answers (1)

Related Questions